1. Field of the Invention
This invention relates to graphic display devices used as terminal devices for data processing systems wherein a central computer supplies data to be graphically displayed, e.g., upon a cathode ray tube.
2. Description of the Prior Art
Graphic display devices using a cathode ray tube (CRT) with a raster scan system for developing characters have been in use for a number of years with general purpose digital computers. Such devices have an alphanumeric character generator which stores data regarding the formation of the vocabulary of characters to be drawn upon for display, and a refresh memory which stores data designating the particular arrangement of characters to be displayed on the CRT. Typically, the character generator employs a read-only-memory (ROM), and the number of characters, numerals or symbols available for display on the CRT is limited by the memory capacity. Increasing memory capacity to allow storage of more alphanumeric data is expensive. For various reasons a satisfactory solution to this problem has not been found.